Steam activation reaction for production of activated carbon or active charcoal is ordinarily performed by causing steam to react on starting or feed carbon at a high temperature of 750-950° C. to result in fine pores in the feed carbon through water gas reaction, thereby producing activated carbon. As the apparatus for producing activated carbon, a rotary kiln, a moving bed, a fluidized bed, etc., have been conventionally used. Among these, a fluidized bed is characterized by a fast heat-exchange speed to provide a uniform particle temperature as a whole. Accordingly, a batchwise operation thereof affords a uniform reaction in the entire apparatus and can obviate unnecessary waste of carbon even in the case of production of a highly active activated carbon requiring a long reaction time through a uniform conversion free from a fraction of insufficient conversion or a fraction of excessive conversion, thus allowing the production of activated carbon at a high yield for an identical conversion.
The batchwise operation affording a further uniform reaction time requires such an operation as to initiate the reaction by heating the furnace after feeding the starting carbon and discharge the activated carbon, after cooling the furnace after the reaction. This requires the raising and lowering of the apparatus temperature for each batch, thus resulting in much loss of time and energy. Further, the temperature change causes heat stress distortion, thus being liable to cause problems such as deterioration of furnace structure and materials.
These problems can be alleviated by a continuous operation, which however is accompanied with a mixing state in the fluidized bed close to a complete mixing state, thus resulting in a product including a mixture of different conversion fractions. For preventing the problem by minimizing the mixing in the process flow direction to provide a residence time distribution in the apparatus, it has been known effective to divide the apparatus into a series of multiple stages (Terukatsu MIYAUCHI, Shin Kagaku Kohza (New Chemical Lecture) 14, “Ryu-kei Sousa to Kongoh Tokusei (Flow-system Operation and Mixing Properties), pp. 14-18 and p. 24, published from Nikkan Kogyo Shinbunsha (1960)). However, in order to obtain a uniform conversion as obtained by a batchwise operation, a large number of stages as many as several tens of stages, is required and is not realistic.
JP49-91098A discloses a process for continuous production of activated carbon using a vertical multi-stage fluidized bed apparatus partitioned by a plurality of perforated partitioning plates. More specifically, utilizing a phenomenon that the particle size of feed carbon is reduced along with the progress of activation reaction, JP49-91098A uses a continuously operated fluidized bed furnace in which horizontal perforated partitioning plates having perforations at a size of 2-4 times as large as a maximum particle size of the feed carbon at an aperture rate of 20-30% are disposed and the feed carbon is fluidized at a velocity of several times the minimum fluidization velocity of the feed carbon. The JP reference describes that, as a result thereof, each stage of activation chamber is provided with a certain length of space between a stack portion of carbon particles and a horizontal perforated plate immediately thereabove, and carbon particles caused to have reduced sizes due to progress of activation in the fluidized bed are selectively and consecutively transferred to above the partitioning plate, thus providing activated carbon having a very narrow distribution of residence time, i.e., reaction time. However, if this process is applied to production of a high-performance activated carbon having a high degree of activation, it has been found that the activated carbon cannot be obtained at a desired yield (as shown in Comparative Example 2 appearing hereinafter).